I wrote a paper on this for school (its in dutch, but maybe a translation-tool can make it funny) and around the same time I built my own device. The source I used for my paper ("Perpetuum mobile; or a history of the search for self-motive power, from the 13th to the 19th century" by Henry Dircks) explains how every idea fails at a certain point, followed by a lot of effort and time of its creator to tweak, fine-tune and adapt the original idea...
The same for my idea, shown here. It's based on shifting its weight to one side, so it will start to rotate (clockwise). Pulling in the extended weight at the bottom... hoping to create perpetual motion... hoping... waiting... tweaking, fine-tuning and adapting... ;-)